1. Field of the Invention
The invention relates to an image forming apparatus such as a color printer or the like.
2. Related Background Art
In an image forming apparatus such as an electrophotographic printer or the like, image information sent from an upper apparatus is converted into print data. In the image forming apparatus, a photosensitive drum is charged to a negative polarity by a charging roller and an electrostatic latent image of the print data is formed by an LED head. A toner image is formed onto the electrostatic latent image by using a developing roller, a toner conveying roller, a developing blade, and the like. The toner image is transferred onto a print sheet by a transfer apparatus. Toner remaining on the photosensitive drum in those steps is removed by a cleaning apparatus.
In a color electrophotographic printer or the like, a black image drum, a yellow image drum, a magenta image drum, and a cyan image drum are provided in correspondence to colors of K (black), Y (yellow), M (magenta), and C (cyan), respectively. Those four image drums are attached to predetermined positions in the image forming apparatus. The print data of a predetermined color is transmitted to each of the four image drums. The four image drums reproduce images based on the respective print data onto the print sheet. A color image is reproduced in this manner. In such a conventional color electrophotographic printer or the like, a technique for separating the print data into image data, figure data, and character data and effectively reproducing a monochromatic image or the like and the like have already been opened (for example, refer to an abstract of JP-A-10-289079).
In the above conventional color electrophotographic printer or the like, in the case of receiving color image information and printing a color image only in two colors, a data process for preventing a deterioration of expressing ability is necessary. Even in the case of reproducing the image in two colors, in order to execute the printing operation, all of the four image drums for the colors of Y, M, C, and K need to be attached to the predetermined positions in the image forming apparatus. Therefore, since the image drums which are not used for the 2-color printing are also held in the operative mode, their lives are shortened. Further, those predetermined positions are preset positions and cannot be changed. Thus, such a problem to be solved that in the case where a part of the character data is emphasized by using another color or the like, even when another color is not limited to a certain color, it is difficult to continue the printing of only two colors for a long time still remains.